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PRELIMINARY METHOD 001 - 6/19/86

PRE-001

METHOD _ - DIRECT MEASUREMENT OF GAS VELOCITY AND VOLUMETRICFLOWRATE UNDER CYCLONIC FLOW CONDITIONS (PROPELLER ANEMOMETER)

1.Applicability and Principle

1.1 Applicability. This method applies to the measurement ofgas velocities in locations where cyclonic flow conditions existand gas temperatures range from O° to 50°C (e.g., cooling tower

exhausts).

1.2 Principle. A propeller anemometer is used to measure gasvelocity directly. The area of the stack cross section at thesampling location is used to calculate volumetric flowrate, andtemperature and pressure measurements are used to correct volumes

to standard conditions.

2.Apparatus

Specifications for the apparatus are given below.

2.1 Propeller Anemometer. A vane axial propeller anemometercapable of measuring gas velocities to within 2 percent. The

manufacturer’s recommended range (all-angle) shall be sufficientfor the expected minimum flow rates at the sampling conditions. Temperature, pressure, moisture, corrosive characteristics, andsampling locations are factors necessary to consider in choosing

a suitable propeller anemometer.

2.2 Data Output Device. A digital voltmeter, analog voltmeter,stripchart recorder, data-logger, or computer capable of

displaying a propeller anemometer output to within 1 percent andat a minimum frequency of one reading per minute.

2.3 Temperature Gauge. Same as Method 2, Section 2.3 for volumecorrection to standard conditions.

2.4 Barometer. Same as Method 2, Section 2.5 for volumecorrection to standard conditions.

2.5 Calibration Equipment.

2.5.1 Synchronous Motor. A variable speed synchronous motorcapable of providing a known constant rotational speed to the

input shaft of the propeller anemometer for purposes of comparing

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and adjusting the output signal to known values.

2.5.2 Bearing Torque Disc. A variable torque applicator capableof applying a range of torques to the input shaft of the

propeller anemometer from zero to the manufacturer’s recommended“poor performance” criterion.

2.5.3 Wind Tunnel. A wind tunnel capable of providing stablevelocities over the expected range of velocities to be measured. Air flow should be fully developed turbulent flow in the axialdirection only. Means shall be available to quantify ambient

temperature and pressure for correction to standard conditions. Means shall also be available to rotate the propeller anemometer,within the wind tunnel, through 180° (±90E of the centerline) and

note the angle of rotation in 10E increments.

2.5.4 Calibration Pitot Tube. Same as Method 2, Section 2.7 fordetermination of wind tunnel velocities to within 1 percent.

2.5.5 Differential Pressure Gauge for Calibration Pitot Tube. Same as Method 2, Section 2.8 for use with the standard pitot

tube during wind tunnel velocity determinations.

3.Procedure

3.1 Proper Mounting of Propeller Anemometer. Attach thepropeller anemometer to a suitable device (probe, rail, rod,etc.) To facilitate traversing the stack/duct cross-section. Ensure that all flow obstructions created by (1) the samplingsupport equipment (rail, etc.) are a minimum of two propellerdiameters downstream of the propeller and (2) the sampling

equipment (nozzles) are a minimum of 2 inches upstream of thepropeller and have a maximum obstructive area (projected area )10 percent the size of the propeller’s area of rotation. Ensure

that the propeller anemometer is properly aligned with thecenterline of the stack/duct and stably mounted (vibration and

subsequent misalignment will create serious errors in thevelocity and volumetric flow rate results). Connect electricalconnections for velocity data recording as shown in Figure PA-1.

3.2 Cross Sectional Area. Determine the stack/duct dimensionsat the sampling location. Include the total area (at the

sampling location) without regard to the velocity in the stack.

3.3 Zero Output System. Zero all recording devices by carefullybring the propeller anemometer to a standstill. Record ambient

temperature and pressure data and note time and date as

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shown in the example data sheet Figure PA-2.

3.4 Determination of Gas Velocity. Measure the gas velocity andtemperature at the traverse points specified by Method 2 or otherapplicable method. (Note: Due to the size of most propellers,

traverse points within 10 cm of a sidewalk will be unmeasurable.) Alternatively, based on the preliminary traverse or the previousmeasurement, the stack temperature may be measured at a single

point if the gas temperatures at all points are within 5EF of theaverage temperature.

4.Calibration

4.1 Propeller Anemometer. The propeller anemometer shall becalibrated before its initial use in the field. Both

electro/mechanical and performance parameters shall be checkedduring calibration according to the procedures supplied by themanufacturer. Calibration procedures in 4.1.1, 4.1.2 and 4.1.3shall be conducted before the initial field use. Calibration

procedures in 4.1.3 shall be conducted for each propeller in useand whenever the structural integrity of a propeller or

shaft/generator housing is in question.

4.1.1 Generator Output Test. To assess the integrity of theelectrical output, a variable speed synchronous motor to rotate

the propeller anemometer input shaft at known rotationalvelocities will be required. A minimum of two speeds shall beused to check the electrical output of each shaft/generator

housing. The two speeds chosen shall fall on either side of theexpected shaft velocities under field use.

Couple the synchronous motor to the anemometer input shaftaccording to the manufacturer’ specifications (to ensure noslippage occurs). Attach an output device to the anemometerelectrical outputs and start the motor. Obtain the first

rotational test speed and record the anemometer output in eithermV DC or rpm. Obtain the second rotational test speed and recordthe anemometer output. Continue with additional rotational testspeeds if applicable. Repeat each test speed in order to obtain

a total of three output readings for each speed.

Average the three output readings from each rotational test speedapplied and compare these results with the manufacturer’sspecifications (e.g., linear rpm/mV ratio). Results should

compare with specifications to within 2 percent.

4.1.2 Bearing Torque Test. To assess the integrity of themechanical bearings supporting the input shaft, a bearing torque

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FIGURE PA-2. EXAMPLE VELOCITY AND VOLUMETRIC FLOWRATE DATA SHEET

Plant/Location

Date Run

Operators Time (start/finish

Stack/duct dimensions m (in.)

Cross sectional area m (in. )2 2

Anemometer ID no. Calibration Date

Anemometer electromechanical rotation

Anemometer axial/rotational velocity ratio

Ambient Temperature EC (EF) Barometric Pressure mm Hg (in. Hg)

Traverse Stack/Duct Temp. Anemometer Output Gas Velocitypoint v , m/s (A/s)no.

st , EC (EF) T , EK (ER) V , mV v , rpms s a r

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test shall be conducted. Attach a torque applicator (e.g., bearing torquedisc) to the anemometer input shaft which will apply a range of known,

repeatable torques beyond the manufacturer’s “poor performance” criterion. Starting with a 0.1 gm-cm torque, continually increase the applied torque

in 0.1 gm-cm increments until the shaft begins to turn. Record the appliedtorque required to create shaft rotation and repeat two times. Results

from all three tests should be below the manufacturer’s specification for“poor performance.” Conduct this check after the non-axial flow

calibration to document the torque required during the calibration.

4.1.3 Non-Axial Flow Test. Assess the representativeness of themanufacturer’s angular flow calibration curve by conducting a wind tunneltest on each propeller in use and generating a percent response-vs-windangle curve for comparison. Attach the propeller anemometer to the wind

tunnel to allow a full 180E rotation (±90E from the center line) within thetunnel. Connect all other apparatus to display/record anemometer outputs.

With the wind tunnel operating at 15 to 25-fps, determine the velocity atthe propeller location using a standard pitot and a differential pressuregauge. Record the barometric pressure and temperature. Starting with thepropeller anemometer oriented into the direction of flow (0E) rotate andrecord the output readings at 10E increments from 0E to +90E and 0E to -90E. Plot these results on a percent response-vs-wind angle graph and

compare to the manufacturer’s specifications. Differences should be within3 percent at each point for the 100 percent axial flow response. Using the100 percent axial flow response, compute a velocity result and compare itto the velocity results measured using the standard pitot probe. Thisdifference should be with 3 percent of the pitot probe results at 0E. Repeat this test at a velocity of 25 to 40-fps; compute the percent

deviations as above.

Note: If the results of the propeller anemometer initial calibration testsare not with the required specifications, then either corrective

maintenance should be implemented to correct the deficiencies or theequipment in question should be considered unsatisfactory and replaced.

4.1.4 Field Use and Recalibration.

4.1.4.1 Field Use. When the propeller anemometer is used in the field,the manufacturer’s electromechanical ratio and axial/rotational velocity

ratio shall be used to perform the velocity calculations.

4.1.4.2 Recalibration. After each test run, both a bearing torque checkand a generator output test shall be conducted. If the bearing torque

check is more than twice the torque recorded after the calibration or is inthe range of “poor performance” as described by the manufacturer, theanemometer must be repaired or replaced and the run repeated. The

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generator output test results must be with 5 percent of the predicted valueor the system must be repaired or replaced and the run repeated.

Alternatively the tester may opt to conduct both checks at the conclusionof all runs. However, if both criteria are not met, all runs must be

repeated.

If both checks meet the above criteria and a visual inspection of thepropeller shows no apparent changes, no additional calibrations must be

conducted. Whenever the propeller anemometer fails to meet of either theabove requirements or the propeller becomes damaged, a complete

recalibration as described in 4.1.1, 4.1.2 and 4.1.3 must be conducted.

4.2 Temperature Gauge. After each test series, check the temperaturegauge at ambient temperature. Use an American Society for Testing and

Materials (ASTM) mercury-in-glass reference thermometer, or equivalent, asa reference. If the gauge being checked does not agree within 2 percent

(absolute temperature) of the reference, the temperature data collected inthe field shall be considered invalid or adjustments of the test results

shall be made, subject to the approval of the Administrator.

4.3 Barometer. Calibrate the barometer used against a mercury barometerprior to the field test as described in Method 2.

5.Calculations

Carry out the calculations, retaining at least one extra decimal figurebeyond that of the acquired data. Round off the figures after the final

calculation.

5.1 Nomenclature

A =Stack cross-sectional area, m .s2

C =Constant, anemometer manufacturer’s electromechanical ratio, rpm/mV.e

C = Constant, anemometer manufacturer’s axial/rotational velocity ratio,r

cm/rev.P =Barometric pressure, mm Hg.bar

P =Average static pressure, mm Hg.g

=Volumetric flowrate at standard conditions (20EC and 760 mm Hg), m /min.Q.s.3

T =Absolute stack temperature, EK.s

t =Stack temperature, EC.s

V =Anemometer voltage output, mV.a

v =Rotational velocity, anemometer output, rpm.r

v =Stack gas velocity, m/sec.s

5.2 Velocity.

v =C V (Eq. PA-1)r e a

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v =C v /100(Eq. PA-2)s r r

=C C V /100r e a

5.3 Volumetric Flow Rate.

Q =A v (Eq. PA-3)s s s

=60 A C C V /100s r e a

6.Bibliography

1. Gill, G.C., H.W. Carson, and R.M. Holmes. A Propeller-Type Vertical Anemometer. J. Applied

Meteorology, December 1964.

2. Gill, G.C. The Helicoid Anemometer. Atmosphere, Vol. 11, No. 4,1973.